Fuel Nozzle Metering Valve With Dribble Flow at Low Pressure
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Solution Overview
Problem
At low engine speeds, fuel nozzles in aircraft combustion engines face challenges in maintaining fuel flow to the combustion chamber due to low pressure drops, which can lead to engine flameout if not addressed.
Innovation Solution
A metering valve with a dribble flow feature is introduced, allowing fuel to flow through the nozzle before the main valve opens, ensuring continuous fuel supply and preventing engine flameout by creating a clearance or thinning in the spool and liner design.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a metering valve is used to protect against pressure variation at low flows, then fuel flow control is improved, but fuel flow is blocked at ignition until pressure builds up
Solution Approach 1:
The metering valve is segmented into two distinct flow paths: a main flow path controlled by the metering valve for pressure regulation, and a separate dribble flow path that remains open during ignition. This segmentation allows the valve to provide both flow control and continuous fuel delivery during the critical ignition-to-idle transition.
Solution Approach 2:
A dribble flow passage acts as an intermediary path that bypasses the closed metering valve during ignition. This intermediary channel ensures continuous fuel flow to the combustion chamber even when the main metering valve is seated, eliminating the flameout risk while maintaining pressure control capability.
2Stability of the object's composition
If the metering valve is seated to control pressure variation, then pressure stability is improved, but fuel flow to combustion chamber is insufficient
Solution Approach 1:
The flow control system is divided into two independent channels: a pressure-controlled main flow path and a pressure-independent dribble flow path. The dribble path maintains stable fuel quantity delivery during ignition regardless of pressure fluctuations, while the main path provides pressure stability when open.
Solution Approach 2:
Different regions of the metering valve assembly provide different flow characteristics: the main valve seat area provides pressure-regulated flow with high stability, while the dribble flow passage provides unrestricted flow with adequate quantity during the critical ignition phase.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The dribble flow feature significantly reduces or eliminates the risk of engine flameout during the transition from ignition to idle by maintaining fuel flow at low pressure drops, enhancing engine stability and reliability.
Implementation Method 1
pressure drop across the nozzle is low, which makes maintaining fuel flow into the combustion chamber comparatively more difficult
Implementation Method 2
provides fluid communication between the inlet and the orifice when the spool is in the lifted off position
Data Source
AI summary
Embodiments of a metering valve for a fuel nozzle are disclosed. The metering valve includes a fitting having an interior cavity and an inlet, a liner disposed within the interior cavity, and a spool having an orifice. The liner includes inlet ports, and the spool is disposed within the liner. The spool is configured to slide within the liner to control flow between the inlet and the orifice. The spool has an open position in which the spool uncovers the inlet ports, a closed position in which the spool is seated against the fitting, and a lifted off position in which the spool is not seated against the fitting and covers the inlet ports. A dribble flow path through at least one of the spool or the liner provides fluid communication between the inlet and the orifice when the spool is in the lifted off position.